Whereas a bidirectional bubble transfer switch is required in contiguous disk devices having a single major loop for both read and write transfer functions, a one-way switch is preferred when separate read and write major loops are employed. Better performance is expected from switch designs specialized for transfer in one direction.
A problem with separate read/write major loops using one-way transfer switches is data reversal. Data reversal results because ion-implanted tracks only propagate bubbles on the implanted side of the boundary and because the implanted side of the read major loop and the write major loop face each other. A number of approaches have been proposed to rearrange the data. One such data rearrangement switch was described by Keefe et al in the IBM Technical Disclosure Bulletin Vol. 23 No. 6 November 1980, pp 2595-2597. While this proposal did solve the data reversal problem, it had the disadvantage of requiring an idler loop which occupied extra area on the bubble chip.
Another approach to the data reversal problem was described by Nelson et al in a Bell System Technical Journal Vol. 59 No. 2 February 1980 article on pages 229-257 and is shown in FIG. 1. A one-way transfer switch 10 is described in which a wavy or snake-like major loop 12 has a hairpin conductor 14 positioned thereon so that a bubble was stretched through the major loop, i.e. from the cusp on side 16 to the tip on side 18, and then from the major loop track to the end 20 of the minor loop 22. In this design the original side 16 of the major loop track 12 is designed to be attractive and the opposite side 18 to be repulsive after the bubble is stripped through the boundary. This is as a result of the relative position of the major loop side 18 and minor loop end 20. Then the bubble moves again to the attractive position at the end of the minor loop with the help of the hairpin conductor. The phase margins with this switch are poor since they are limited by the hairpin conductor which crosses through the major loop propagation path. In addition, this switch is not reliable.